1. Field of the Invention
The invention relates in general to a pneumatic operating mechanism for a circuit breaker and in particular to a means for quickly closing a pneumatically operated trip valve of the operating mechanism.
2. Description of the Prior Art
Fast acting circuit interrupters may employ pneumatic operating mechanisms, such as are described in U.S. Pat. Nos. 4,095,068, 4,101,748 and 4,213,020, all of the aforesaid patent applications being assigned to the assignee of the instant patent application. These pneumatic operating mechanisms may employ a multiple pneumatic valve relay arrangement to open a large pneumatic trip valve, which quickly applies high pressure compressed air to a movable driving piston, which is mechanically linked to and urges the interrupter contacts opened and closed. After operation, it is important to close this large pneumatic trip valve as quickly as possible to prevent excessive air consumption and corresponding pressure drop in the air reservoir. A method utilized in the prior art for closing the large trip valve was to have a bleed-off orifice in the actuating cylinder which is used to open and close the trip valve. In order to insure quick operation of the pneumatic operating mechanism and positive positioning of the breaker contacts, however, it is necessary for this bleed-off orifice to be sized small, which causes the air to be eliminated through it slowly, causing the trip valve to remain open unnecessarily long causing excessive air consumption through the movable driving piston cylinder. Accordingly, it would be desirable to have an economical means for quickly eliminating the air from the pneumatic trip valve actuating cylinder while insuring positive positioning of the breaker contacts during the opening operation.